Siham, wife of Mohammed Darrar Jammo, a Syrian political analyst and one of Syrian President Bashar Assad’s strongest defenders who was gunned down inside his home, mourns her husband, in the southern coastal town of Sarafand, Lebanon, Wednesday.

BEIRUT — Gunmen burst into the first floor apartment of a pro-government Syrian journalist Wednesday, killing him in a hail of nearly 30 bullets in a Hezbollah stronghold in southern Lebanon.

The pre-dawn assassination of Mohammed Darrar Jammo is the latest in a series of brazen attacks that have shown the growing vulnerability of the Shiite militant group, which has found itself increasingly on the defensive at home over its decision to back President Bashar Assad in the civil war raging next door.

Violence linked to Syria’s war is increasingly washing across Lebanon, threatening to unleash large-scale fighting in a deeply fragmented country that is being constantly tested with ever deepening polarization over the conflict in Syria.

In recent months, violence has become more recurrent and geographically widespread, extending to predominantly Shiite neighborhoods that had been relatively immune from attacks plaguing other, mostly border areas.

On Tuesday, a roadside bomb struck a Hezbollah convoy near the Syrian border, wounding two, and last week a car bombing in south Beirut wounded 53 people in the heart of the militant group’s bastion of support. Rockets have recently hit the Hezbollah stronghold south of the Lebanese capital.

The attacks come as no surprise. Although there have been no credible responsibility claims, Syria-based extremist Sunni groups have interpreted Hezbollah’s moves in Syria as a declaration of war against their sect and have threatened to retaliate inside Hezbollah-controlled areas in Lebanon.

“It is still the beginning of a probably tough road ahead” for Hezbollah, said Kamel Wazne, founder and director of the Center for American Strategic Studies in Beirut. Such attacks, however, will not change the group’s ideology or direction, but “will actually strengthen their resolve to continue what they started,” he said.

Jammo, a 44-year-old journalist and political commentator, was one of Assad’s and Hezbollah’s most vociferous defenders. In frequent appearances on television talk shows, he would staunchly support the Syrian regime’s strong-armed response to the uprising and in at least one case shouted down opposition figures, calling them “traitors.”

His hard-line stance earned him enemies among Syria’s opposition, and some in the anti-Assad camp referred to Jammo as “shabih,” a term used for pro-government gunmen who have been blamed for some of the worst mass killings of the civil war.

On Wednesday, he was gunned down with automatic rifles shot at close range in his apartment in the coastal town of Sarafand, a stronghold of Hezbollah, where he lived with his Lebanese wife. The perpetrators got away.

Lebanon’s state news agency published a photo Wednesday of a shirtless Jammo lying on a blue sheet soaked with blood, his chest riddled with bullet wounds. Bullet holes were clearly visible in the walls inside the house.

Hezbollah condemned the attack, saying it showed the “bankruptcy” of Sunni extremist groups fighting in Syria. In a statement, it said that the crime should serve as an “alarm bell” for Lebanese authorities “to find the most appropriate way to confront these terrorist groups before it is too late.”

Assassinations of politicians, army officers and journalists who support Assad’s regime are common in Syria, but the killing of a well-known Syrian in Lebanon is rare.

Syria’s conflict has cut deep fissures through Lebanon and exposed the country’s split loyalties. Many Lebanese Sunnis support the overwhelmingly Sunni uprising against Assad, while Shiites generally back Hezbollah and the Syrian regime.

Clashes between pro- and anti-Assad groups in Lebanon have left scores of people dead in recent months, and the violence has escalated as Hezbollah’s role fighting alongside the Syrian regime has become public. The group was instrumental in helping secure a regime victory in the strategic town of Qusair near the border with Lebanon last month.

Naufal Daou, a member of the anti-Hezbollah political coalition in Lebanon, said that by defying the will of the Lebanese people, Hezbollah finds itself facing a real dilemma “inflicted on itself by its stubbornness ... and insistence to attach Lebanon’s fate to that of rogue states and dying political regimes.”

The slide in Lebanon toward violence is taking place amid a dangerous political void. Politicians have been unable to form a new government since outgoing premier Najib Mikati resigned in March. Parliament extended its mandate by a year and a half in June, skipping scheduled elections largely because of the instability in the country.

The country appears to be headed toward a security vacuum in September, when the term of army commander Gen. Jean Kahwaji expires. Politicians are divided over whether parliament should meet to extend his mandate.

Analysts say Hezbollah is unlikely to be affected by the wave of attacks targeting its strongholds.

“Hezbollah is very good at taking punches,” said Wazne. He said the group feels stronger and more assured now that Assad has regained the momentum against rebels fighting to topple him, largely after the fall of Qusair.

Hezbollah’s hard-core Shiite supporters are likely to rally further around the group following such attacks.

In other developments Wednesday, Kurdish gunmen captured most of a Syrian town near the border with Turkey after a day of fighting against jihadi groups in the area, the Britain-based Syrian Observatory for Human Rights said. Such clashes have been common over the past months in rebel-held areas in northern Syria.

The Observatory said the fighting in the town of Ras al-Ayn between the pro-government militia of the Kurdish Democratic Union Party, or PYD, and members of al-Qaida-linked Jabhat al-Nusra and the Islamic State of Iraq and the Levant left at least 11 dead people dead, including nine extremists.

Stray bullets from the fighting killed a 17-year-old in a Turkish town, a Turkish official said. Turkey’s military said it fired into Syria in retaliation for the killing.

The fighting broke out Tuesday after the Islamic fighters attacked a Kurdish patrol in the area, capturing a Kurdish gunman. Wide clashes broke out later in the day after the two extremist groups rejected a truce offer, according to the Observatory.

Syrian TV reported Wednesday that a car bomb went off near a mosque in the Damascus suburb of Kanakir, killing three people and wounding 10 others, including women and children.